When agriculturally active chemicals (agrochemcials) are relatively water soluble, preparing, storing, and shipping the same in a commercially acceptable form can be relatively clear-cut. However, many agrochemicals are hydrophobic and formulators are often confronted with difficulties in finding a suitable means for preparing these materials in stable formulations that deliver maximum loading of active ingredient per unit volume to the end-user. One means of doing this is to prepare dry formulations such as wettable dispersible granules (WDG's) or wettable powders (WP's) encapsulated, for example, in water soluble bags or containers. Although such dry formulations are attractive not only from a loading delivery viewpoint, but also from a handling and/or worker safety viewpoint, not all hydrophobic agrochemicals are able to be dry formulated.
The most straight-forward approach to preparing concentrated liquid formulations with agrochemicals having limited aqueous solubility has been through the use of aromatic organic solvent systems. In such systems, aromatic organic solvents such as xylene or kerosene are used to solubilize the agrochemical compound of interest.
Commonly, surfactants are added to the agrochemical-solvent compositions to form emulsion concentrates. The surfactant-emulsifiers interact with the agrochemicals in a number of ways both before and during actual use, i.e., application to the site. The surfactants can initially disperse and/or emulsify the agrochemical in the solvent or in an inert carrier media and, for example, with herbicides, the surfactant composition may also act as a penetrant, spreader, sticker, stabilizer, and wetting agent. The surfactant composition may affect the rate of drying of a droplet on a plant and the nature of a residue liquid, or crystal. The surfactants may also influence the weathering characteristics of an agrochemical, including its rewetting characteristics and rainfastness.
The presence of the volatile organic compounds in these formulations, together with the surfactants, enable stable emulsifiable agrochemical concentrates (EC's) to be prepared. Although such EC formulations have played and continue to play a major role in the agrochemical market, they have a significant drawback in that the formulations are commonly based on the use of considerable quantities of the highly volatile organic compounds. Some of these highly volatile organic compounds are not entirely satisfactory; in particular with respect to their ecological and toxicological properties. One additional characteristic, which is growing in importance in the agricultural chemical marketplace, is the property of reduced eye irritation as measured by published U.S. Environmental Protection Agency regulations.
Microemulsion (ME) technology has been explored as a possible approach to address the above-noted drawbacks of agrochemical EC formulations. In general, microemulsions are characterized by particle sizes between 3 and 10 nm. The small particle size allows for the emulsion to be more stable than an EC formulation. These systems have proven highly useful for such diverse objects as surface cleaners, paint compositions, oil recovery systems, cosmetic preparations, drug delivery and pesticidal formulations. The desired properties of these compositions are obviously quite varied depending on the intended application, but all of these compositions have the advantage of limited use of undesirable solvents and formation of a highly stable emulsified form.
There is still a need for further microemulsifiable agrochemical concentates that are suitable for a broad range of agriculturally active ingredients, have a high biological activity in the target application, have good chemical and physical stability under a severe range of conditions that can be experienced in the marketplace, have good ecological and toxicological properties, exhibit reduced eye irritation and be readily water-dilutable to form a microemulsion.